Heat pipe heating system for a railway tank car or the like

ABSTRACT

A heat transfer pipe containing a vaporizable fluid and having a porous wick on its inner surface is mounted in the tank of a railway tank car and extends into a furnace outside the tank. The outer end of the pipe communicated with a reservoir for the fluid. The wick has a plurality of porous metallic layers designed to provide good heat transfer, as well as a high degree of capillary action. Evaporation of the liquid produced by the furnace and condensation along the whole length of the pipe in the tank transfer a great amount of heat into the tank at a generally uniform temperature.

O Unrted States Patent [111 3,55

[72] Inventors George M. Grover 3,378,449 4/1968 Roberts et al l65/l05XLos Alamos, N. Mex.; 3,468,300 9/1968 Geyer et al. 165/105X Edward L.Coyle, St. Charles, Mo. FORElGN PATENTS [211 APPLNQ 7651208 771,8788/1934 France 165/105 [22] 1968 723,857 8/1942 Germany l65/l05 [45]Patented Jan. 12, 1971 OTHER REFERENCES [73] Assignee ACFlndustries,lncorporated I N Y k,N Y l. Deverall, J. E. et al., HighThermal Conductances acorporation of New Jersey geviciegofl 1965, LosAlamos Scientific Laboratory. pp.

an 2. Sandia Laboratories Heat Pipe Conference 1966 [54] HEAT PIPEHEATING SYSTEM FOR A RAILWAY Albuquerque, N .M., pp 12 and 24 (91pages), SC-M-66-623 Primary Examiner-Albert W. Davis, Jr. gAttorneysSamuel .I. Snyder and Eugene N. Riddle [52] US. Cl. 126/3435,

165/105, 165/134 [51] lnLCl- Bfild /04, ABSTRACT: A heat transfer pipecontaining a vaporizable Fzsd /00 fluid and having a porous wick on itsinner surface is mounted Field ofSearch 165/105, in h tank of a railwaytank and extends into a furnace 134; 126/3435 outside the tank. Theouter end of the pipe communicated 56] R f cted with a reservoir for thefluid. The wick has a plurality of e erences I porous metallic layersdesigned to provide good heat transfer, UNITED STATES PATENTS as well asa high degree of capillary action. Evaporation of the 1,975,868 [0/1934Schlumbohm l/l05X liquid produced by the furnace and condensation alongthe 2,581,347 l/ 1952 Backstrom /105X whole length of the pipe in thetank transfer a great amount of 3,305,005 2/ 1967 Grover et al 165/105heat into the tank at a generally uniform temperature.

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SHEET 1' BF 8- N INVENTORS. 2.3 N GEORGE M. GROVER it EDWARD 1.. COYLEATTORNEY PATENTED JAN 1 2 I97! SHEET 8 OF 8 HEAT ms HEATING SYSTEM FOR ARAILWAY TANK CAR orrrneu a BACKGROUND OF THE INVENTION Heat transferpipes commonly known as heat pipes" comprise an outer enclosed shell, aporous wick, and a working fluid for wetting the wick.A portion of theheat pipe referred to as the evaporator section is heated and theworking fluid in the evaporator area is vaporized and driven through thepipe. As heat is given off by the heat pipe, the vaporized fluidcondenses to a liquid and is re'turned to the boiler areaby the SUMMARYor. THE INVENTION The present invention is directed to a railway tankcar having a heat pipe mounted thereon for heating and maintaining thelading at a predetermined temperature during transit and at unloadingsites. A generally straight length of the heat pipe is mounted withinthe tank and has, an outer end portion extending outwardly of the tankinto a heat producing furnace.

The heat transfer pipe comprises an outer enclosed shell, a porous wickpositioned against the inner surface of the shell, and a vaporizablefluid within the shell, the fluid being vaporized from the'heatgenerated by the furnace and moving and inner tank 12. A center sill 18extends the length of railway car 10, with outer jacket I4 beingattached to the outer sides of center sill 18. A coupler I9 is mountedwithin each end of center sill 18. A wheeled truck 20 is providedadjacent each end of railway tank car 10.

Mounted on an end of railway tank car I0 is furnace 22 of the open flametype. To supply fuel, such as propane gas, to furnace 22, a fuelcontainer 24 is mounted on each side of railway tank car 10 and has afuel line 26 leading to furnace 22. Mounted within inner tank 12 forheating liquid lading therein to temperatures of 500 F. or greater is aheat pipe 28 for transferring heat from 'fumace 22 to the lading withininner tank 12. Heat pipe 28 includes an inner portion mounted withintank 12 and an outer end portion 32 which extends through the adjacentend of inner tank 12 and outer jacket 14 within furnace 22. As shown inFIG. 2, brackets generally indicated 3 4, have sleeves 36 receivinginner heat pipe portion 30 and lower legs secured to the inner surfaceof tank 12 to support heat pipe section 30 within the tank at a heightabove the bottom of the tank. As shown in FIG. 1, heat pipe 28 slopesdownwardly to outer end portion 32 within furnace 22. As it is desirablefor pipe 28 to have such a downwardly slope under all operatingconditions, the slope may preferably be between 2 percent and 4 percent,which is normally the maximum railway grade encountered. Thus, the slopeof pipe 28 outwardly away from the furnace to condense along the lengthof the pipe upon the transfer of heat to the lading within the tank car.Upon condensing, the fluid is returned by the capillary action of thewick to the outerv end portion of the pipe. Sufficient working fluid isput intojthe heat pipe to wet the entire wick and the wick is heldtightly and uniformly against the inside wall of the heat pipe; The.outer end of the heat pipe is connected to a reservoir adapted tocontain all of the vaporizable fluid when the heat pipe is notoperating. To obtain efi'rcient heat transfer and capillary action bythe wick, it is formed of a number of layers of wire mesh and permeablemetal.

BRIEF DESCRIPTION or THE DRAWING The invention is illustrated in theaccompanying drawing, in

which:

FIG. 1, is a side elevation of a railway tank car having a heat pipe inthe tank and extending out of the tank into a furnace.

FIG. 2 is a schematic view of a baffle arrangement to providecirculation beneath the heat pipe to the bottom of the tank.

FIG. 3 is a top plan view of the heat pipe, with a portion of the tankbroken away. v

FIG. 4 is a front elevation oftheheat' pipe and its reservoir. FIG. 5 isa sectional view taken along line 5-5 of FIG. 4. FIG. 6 is a partialsectional view along line 15- 6 of FIG. 5. FIGS. 7 and 8 are sectionalviews of portions of another em bodiment of the heat pipe.

FIGS. 9 and I0 are enlarged sectional views of the evaporator andcondenser portions of the heat pipe shown in FIG. 5.

FIGS. I1 and 12 are partial sectional views of another variation of theheat pipe.

FIGS. 13 and 14 show another modification of the condenser section ofthe heat pipe.

FIGS. 15 and 16 are partial views of the furnace and evaporator sectionof the heat pipe.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, aninsulated railway tank car is generally indicated 10 in FIG. I andcomprises an inner tank 12, and outer jacket 14 extending about thecircumference of tank 12, and a layer of insulating material 16, stichas a polyurethane foam material or fiber glass, between outer jacket 14under operating conditions may vary from around 0 to an 8 percent slopedepending on the grade of the railway track.

Referring now to furnace 22 and more particularly to FIGS. 15 and 16, anouter housing 38 extends downwardly to a horizontal section 42 beneathcenter sill I8 as shown in FIG. 15. Fuel lines 26 from fuel containersor tanks 24 lead to burner nozzles 44 suitably mounted within furnace22. Positioned above nozzles 44 are a plurality of vanes or tins 46secured about outer end portion 32of heat pipe 28. A bearing 48 supportsouter end portion 32 and is secured between tank 12 and furnace 22.

Extending upwardly from horizontal section 42 is an inner housinggenerally indicated 54 and forming an air outlet conduit. An upper capor cover generallyindicated 62 is positioned over the upper end ofhousing 54 to prevent foreign matter and rain from entering outletconduit or duct formed by inner housing 54. The air and gas mixtureburns below fins 46, and the heat passes upwardly through the spacedfins 46 to heat pipe section 32. Fins 46 are at a temperature of around700 800 F. The construction of the furnace and the portion of the heatpipe therein are more fully shown and described in application 663,342,mentioned above.

Referring to FIGS. 3 to 6, 9 and 10, heat pipe 28 may have an insidediameter of about 3 inches, and it is welded to a reservoir 70 in theform of a transverse stainless steel pipe located beyond the furnace andextending across one end of the car. The heat pipe is closed by anentl'cap 72. Reservoir 70 has a nipple 73 through which it is chargedwith liquid and an inert gas, such as argon, and has a safety head 74,including a rupture disc, for relieving excessive pressure. The far endof the heat pipe has a welded end cap 76 provided with a stainless steelfiber plug 78, for providing capillary action and insulation at the end.As shown in FIG. 10, pipe section 32 is joined to reservoir 70, and theconstruction in the area marked 10 on FIG. 5 includes a ring 80 ofnickel coated copper, sintered fiber porous material, or other feltedporous metal, held by a snap ring 82, and two layers of rolled orpressed tine mesh stainless steel wire screen 84 folded along the wallof the reservoir as indicated at 86. Beneath screens 84 there are a pairof layers of similar screen 88, and between screens 88 and the wall ofpipe section 32 are eight layers of screen 90 of coarser mesh, forming alayer about a quarter of an inch thick. These several screens constitutethe wick at the evaporator and of the heat pipe.

FIG. 9 shows the construction of the wick in the region marked 9 in FIG.5. Wire screens 88 form the two top layers of the wick. The eight coarselayers of screen 90 are reduced to four layers, which are feathered outas shown, leaving eventually two layers of screen 88, 92 separated fromthe wall of pipe 30 by a corrugated screen 94, best shown in FIG. 6.This wick structure extends out to the end of the pipe. The wick is heldin place by coil spring 96, which is anchored to pin 98 on ring 100 atone end, and anchored to spring clip 102 at the other end. Corrugatedscreen 94 provides large pores for longitudinal flow, while at the sametime maintaining some wicking action, which is primarily provided bysurface layers 88, 92.

FIGS. 7 and 8 show a variation of the wick structure. At the evaporatorend, as shown in FIG. 8, the construction is similar to that of FIG. 10,except that beneath the four layers of screen 110, which may have a 50by 250 mesh, there is a layer 112 of felted metal about one-tenth inchthick, extending throughout the evaporator section of the heat pipe. Inthe condenser section the layer 112 is replaced by a corrugated screen114, which may be similar to that shown in FIG. 6, holding severallayers of fine mesh screen 116 spaced from the wall of the heat pipe.The coil spring 96 for holding the wick against the wall of the pipe maybe the same as coil spring 96 of FIG. 5. Adjacent screens are overlappedas indicated at 115. To prevent shifting of corrugated screen 114relative to the porous metal sheet 112, they are both welded to wirescreen 1 17.

FIGS. 11 and 12 show a wick which, in the evaporator portion, may be thesame as that of FIGS. and 10, including coarse screens 90 and fine meshscreens 88. Along the condenser portion, however, the corrugated screenshown in FIG. 6 is replaced by wide rings 118, 119 of felted metal. Therings 118, 119 are held in place by welding to wire screen rings 120,121. A thin layer of felted metal, including rings 122, 123, are placedon layer 118, 119 and held in place by coil spring 96. The layers 118,119, 122 and 123 are more easily fabricated than wire mesh layers andmay be obtained in cylindrical form. Layer 122, 123 is of fine porosityto provide wicking action primarily, and layer 118, 119 is of largeporosity to provide longitudinal flow paths for the liquid.

Another construction of the wick which may be employed in either thecondenser section 30 or the outer end heat section 32 of the heat pipeis shown in FIGS. 13 and 14. Corrugated sheet metal strips 126 areplaced contiguously to one another, or connected together at theiredges. Matted steel fibers 128 are packed within the corrugations onboth sides of strips 126, and the structure, formed intoa cylindricalsection, is sintered. The sintered fibers provide a highly desirablewicking characteristic when placed on the wall of the condenser section30 of the heat pipe, as shown in FIG. 13, while the metal strips 126provide a very effective heat transfer across the wick. As seen in FIG.14, strips 126 are offset or staggered from one another to provide atortuous flow passage in a longitudinal direction, as well as an annulardirection about the circumference of the pipe. Thus the liquid will benicked from the bottom of the pipe to the upper portion thereof throughthe sintered fiber material having sheet metal corrugations therein.

The operation of the apparatus will be understood by those skilled inthe art, for the principles of the heat pipe have been described in theliterature and patents. Briefly, in the evapora tor or boiler section 32of heat pipe 28, furnace 22 supplies heat to vaporize the liquid, whichmay be water. The vapor moves through the central part of the heat pipe.The lading in the tank car 10 removes heat from the wall of heat pipe 28and causes some of the vapor to condense along the portion 30 of thepipe. The condensate flows back through the heat pipe to evaporatorsection 32, aided by the capillary action of the wick. The great amountof heat energy in the vapor maintains the heat pipe temperature alongthe pipe with a very small gradient. When the heat pipe is not inoperation, the water drains into the reservoir, where no damage iscaused if the water freezes since the reservoir is never full of water.Other features and operational characteristics have been referred toabove and will be understood by those skilled in the art.

I claim: l. A railway tank car comprising a tank shell having ends toform an enclosure for carrying lading, a heat transfer pipe mounted onthe tank car having an inner end portion extending within the tank shelland an outer end portion extending outwardly of an end of said tankshell, and heat producing means mounted on said railway tank caroutwardly of said shell to heat said outer end portion for the transferof heat therefrom to the portion of the pipe within the shell and asubsequent transfer of heat to the lading within the shell, said heattransfer pipe comprising an outer enclosed casing extending axiallygenerally in the direction of the longitudinal axis of the car at aslope of at least 2 percent with respect to the longitudinal axis of therailway car, a porous wick positioned against the inner circumferentialsurface of the casing at least within the outer end portion, avaporizable fluid within the casing, said fluid being vaporized by theheat generated by said heat producing means and moving away from saidheat producing means to said inner end portion, said vaporized fluidcondensing along the length of the heat transfer pipe within the tankshell and returning to the outer end portion by a capillary action ofsaid wick, and a closed sump reservoir of a large cross-sectional arearelative to said casing being outside the tank shell and connected tothe bottom of said outer end por' tion of said pipe for draining off andstoring the vaporizable fluid when said heat producing means is not inoperation, said wick extending along a wall of the reservoir immediatelysub jacent the heat pipe to the bottom of the reservoir whereby thevaporizable fluid may be drained from said reservoir into said pipe by acapillary action, said reservoir having a sufficient capacity to preventdamage to said heat pipe due to freezing of the vaporizable fluid.

2. Apparatus according to claim 1, wherein said reservoir includes anelongated chamber intersecting said heat transfer rpe.

p 3, Apparatus according to claim 1, wherein said wick tapers as itextends from the portion of the pipe in which the fluid evaporates intothe portion of the pipe in which the fluid condenses.

1. A railway tank car comprising a tank shell having ends to form anenclosure for carrying lading, a heat transfer pipe mounted on the tankcar having an inner end portion extending within the tank shell and anouter end portion extending outwardly of an end of said tank shell, andheat producing means mounted on said railway tank car outwardly of saidshell to heat said outer end portion for the transfer of heat therefromto the portion of the pipe within the shell and a subsequent transfer ofheat to the lading within the shell, said heat transfer pipe comprisingan outer enclosed casing extending axially generally in the direction ofthe longitudinal axis of the car at a slope of at least 2 percent withrespect to the longitudinal axis of the railway car, a porous wickpositioned against the inner circumferential surface of the casing atleast within the outer end portion, a vaporizable fluid within thecasing, said fluid being vaporized by the heat generated by said heatproducing means and moving away from said heat producing means to saidinner end portion, said vaporized fluid condensing along the length ofthe heat transfer pipe within the tank shell and returning to the outerend portion by a capillary action of said wick, and a closed sumpreservoir of a large cross-sectional area relative to said casing beingoutside the tank shell and connected to the bottom of said outer endportion of said pipe for draining off and storing the vaporizable fluidwhen said heat producing means is not in operation, said wick extendingalong a wall of the reservoir immediately subjacent the heat pipe to thebottom of the reservoir whereby the vaporizable fluid may be drainedfrom said reservoir into said pipe by a capillary action, said reservoirhaving a sufficient capacity to prevent damage to said heat pipe due tofreezing of the vaporizable fluid.
 2. Apparatus according to claim 1,wherein said reservoir includes an elongated chamber intersecting saidheat transfer pipe.
 3. ApparatuS according to claim 1, wherein said wicktapers as it extends from the portion of the pipe in which the fluidevaporates into the portion of the pipe in which the fluid condenses.